Diamination of Pi-systems Using Simple Urea Derivatives and Exploring Ecologically Relevant Biological Activities Through Natural Products Synthesis
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Diamination of olefins has found broad applications in synthesis of pharmaceuticals and catalysts. Vicinal diamination of olefins has been well developed; however versatile methods that install higher order 1,n -diamine moieties (e.g., n = 3− 5) are not comprehensively explored. We have developed 1,4-diamination of cyclic dienes via diaza-(4+3) cycloadditions of putative diaza-oxyallyl cationic intermediates. This novel intermediate was generated by base-mediated dehydrohalogenation of N-chloro urea reagents. Various aromatic and non-aromatic cylic dienes underwent successfully cycloaddition reaction with diaza-oxyallyl cationic intermediate and provided good to excellent yields. Although it was a first example of selective 1,4-diamination of dienes using N-chloro urea reagents, this methodology suffers from limited substrate scope and poor regioselectivity with mono substituted furans by providing 1:1 ratio of regiosisomers. In order to over come the limitations in our previous method, we have developed an alternative oxidative 1,4-diamination of conjugated dienes using simple urea reagents. The desired putative symmetric diaza-oxyallyl cationic intermediate for the oxidative diaza-(4+3) cycloaddition reaction was generated by direct oxidation of urea reagents with hypervalent iodine reagent. Oxidative 1,4-diamination is exclusively selective for the 1,4-difunctionalization of conjugated dienes due to the required Woodward-Hoffmann orbital symmetry rules. This reaction method is compatible with various substrates including aromatic, acyclic, and cyclic dienes, and provides functionalized unique heterocyclic products. In addition it does not require large excess of diene, which is unusual in (4+3) type of cycloaddition reaction of allyl cations. This reaction also demonstrated its compatibility for oxidative intramolecular 1,4-diamination, and provides polyheterocyclic molecule. Inspired by the reactivity of daiza-oxyallyl cation for 1,4-daimination we have developed an oxidative diaza-(3+2) cycloaddition reaction of simple urea derivatives with substituted indoles. This transformation provides rapid access to highly functionalized imidazolo- indolines that are represented in large number of designed bioactive compounds. This methodology is compatible with wide variety of functional groups and provides unique heterocyclic scaffolds. Plants defend themselves from pathogens like bacteria, viruses and herbivores by using mixture of multiple secondary metabolites as chemical defense. In order to understand one of the long-standing and underexplored questions in chemical ecology, we have developed a scalable access to enantiopure octopamine and aegeline analogues and evaluated the biological assays. These mixtures of products showed synergistic activity in defensive mechanism against generalist herbivore (Spodoptera). One of the natural product (aegeline) analogue exhibited potency against root growth of Arabodopsis Thaliana (a model organism for studying plant cell wall development).